docs: def postprocess_link(self, entry):
          """
          Attempt to load full-text content from resource.
          """
  
          if not self.follow_links:
              return
  
          if type(entry.link) is not list:
              entry.link = [entry.link]
  
          for link in list(entry.link):
              if not os.path.exists(link):
                  continue
  
              mime_type = magic.from_file(link, mime=True)
              if mime_type == 'application/pdf':
                  structuredfeature = extract_pdf(link)
              elif mime_type == 'text/plain':
                  structuredfeature = extract_text(link)
              else:
                  structuredfeature = None
  
              if not structuredfeature:
                  continue
  
              fset_name = mime_type.split('/')[-1] + '_text'
              if not fset_name in self.full_text:
                  self.full_text[fset_name] = {}
  
              if hasattr(self, 'index_by'):
                  ident = getattr(entry, self.index_by)
                  if type(ident) is list:
                      ident = ident[0]
              else:   # If `index_by` is not set, use `uri` by default.
                  ident = entry.uri
  
              self.full_text[fset_name][ident] = structuredfeature